Collimators are well known in the optical arts, and typically include a plurality of lens or reflectors that act upon light to emit nearly parallel rays. Such collimators include searchlights, headlamps and light projectors. A typical example of a light projector designed to emit a collimated beam can be found in U.S. Pat. No. 5,918,968, issued to Choi, which provides a parabolic reflector for converting light emitted from a lamp to parallel rays, a biconvex lens for collimating both direct and reflected light from the light source, a combination lens having a first lens and a second lens for focusing the collimated light from the biconvex lens to a focal point, and an image lens located beyond the focal point for converting the light focused at the focal point into a parallel beam.
U.S. Pat. No. 6,827,475, issued to Vetorino et al., combines a plurality of lens and reflectors to collimate light that includes a conical reflector disposed about the base of a light emitting diode (LED) and a lens specially designed to focus the collected light into a nearly collimated beam. The lens has opposite, substantially elliptical surfaces that collect and collimate the rapidly diverging light from the LED and the reflector. Vetorino et al., however, do not provide for the compression of the collimated beam.
It is also known in the art that the illuminance Lx of a light stream from a light source located perpendicular to an area, illuminates that area according to the following relationship: Lx=Lm/m2. For example, one Lx of illuminance is equal to one Lm of luminous flux for an illuminated surface measuring one square meter in area, and with the light source arranged perpendicular to the surface. In another example, if the luminous flux is equal to 1,000 Lm and the uniformly illuminated surface is one square meter, then the illuminance of that area equals 1,000 Lx. Thus, in order to measure the luminous flux in a uniformly illuminated area of 1.0 square meters, a Lux Meter may be placed anywhere in the illuminated area.
Some prior art producers of light sources, e.g., prior art flashlights utilizing light emitting diodes (LED) claim values of luminous flux (Lm) which in some instances appear higher than the maximum value that can be emitted by the light emitting diode in all directions. Such claims do not account for the uniformity of illuminance (Lx) of an illuminated area where the measurement was taken. Experimentally, the illuminance of two prior art LED's, have been measured and compared to their maximum luminous flux. Two prior art flashlights were chosen for the measurement: (1) ND HB F5, 6V, 2CR 123, 107 Lm Cree LED (hereinafter “HB F5”), and (2) NH HB VIGOUR, 6V, 2CR 123, 107 Lm Cree LED (hereinafter “HB VIGOUR”). Each flashlight having substantially identical electrical specifications, but different optical schematics. The HB F5 appears to utilize an optical schematic that allows for concentrated light emission with uniform luminous flux through the light stream and a +/−2.5° angle of dispersion relative to the optical axis. The HB VIGOUR utilizes a focusing output lens system.
FIGS. 1a and 1b correspond to the illuminated fields of the HB VIGOUR and HB F5, respectively. Although, the illuminated area of fields 1a and 1b were each 1.0 m2, the distance of the flashlights to the illuminated surface varied. HB VIGOUR was located a distance of five meters from the illuminated area, corresponding to illuminated field “1a”; whereas, HB F5 was located a distance of 10.5 meters from the illuminated area, corresponding to illuminated field “1b”. The distribution of illuminance throughout the illuminated fields 1a and 1b is given by Lx=Lm/m2 as illustrated by FIG. 2.
Curve A of FIG. 2 represents the distribution of illuminance of the HB F5 having an illuminated area of 1.0 square meter at a distance of 10.5 meter from the illuminated surface. It can be seen that the maximum luminous flux for curve A is about 135 Lm. Curve B of FIG. 2 represents the distribution of illuminance of the HB VIGOUR having an illuminated area of 1 square meters at a distance of 5.0 meters from the illuminated surface. It can be seen that the maximum luminous flux for curve B is about 80 Lm. Dotted line C of FIG. 2 represents the theoretical maximum luminous flux, 107 Lm, of the LED used in both the HB F5 and HB VIGOUR.
The area under curve A, S1, is calculated as follows: Y=1/√2n exp(−x2/2). Solving for S1 from −56 to +56: ∫[1/√2n exp(−x2/2)]dx=7,795 units. The area under curve B, S2, is 112×80=8,960 units. It can be seen that S1 is smaller than S2, and S1/S2=0.87. Thus, the luminous flux of curve A is equal to 87% of 80 Lm which is 70 Lm, but not 135 Lm as some flashlight manufacturers claim. Thus the uniformity distributed luminous flux cannot exceed the value of 107 Lm because this value is the maximum output of the LED used in both flashlights.
Other light sources include flashlights which typically comprise a light source, a reflector located behind the light source, a lens or glass in front of the reflector, and a power supply. The reflector and the lens are intended to collect light from the source and collimate or focus the light into a desired beam. Such light sources are often portable, and generally produce a diverging beam of light whereby the brightness varies across the beam. Typically, the light beam is brightness at its center, and drops off dramatically at its peripheral edge. Examples of such prior art lights may be found in U.S. Pat. Nos. 1,823,762; 2,228,078; 4,286,311; and 4,527,223.
An important advantage of the present invention is the provision of a light device where the light beam is minimally divergent or compressed along the optical axis, thereby allowing for increased intensity over an illumination range of interest.